Generally speaking, the spindle of machine tools is of either vertical or horizontal type to fit different ways of working as well as different positions of working. A vertical milling machine, for instance, is commonly suitable for vertical milling and drilling work while a horizontal milling machine is normally suitable for lateral milling and drilling work. It is hence necessary to have vertical and horizontal machine tools, respectively, for processing a workpiece in complex form or requiring working in multiple directions. Because of this need, working procedure would become much more complicated, and furthermore, the workpiece has to be held in various positions over and over again thus resulting in loss of working accuracy.
In view of the shortcomings associated with conventional machine tools with only single-action spindle, there has been developments with double-action spindle for vertical-horizontal machine tools. Some machining centers today, for example, have adopted such design of vertical-horizontal spindle. With the design of vertical-horizontal spindle, one single machine tool can thus be provided for the multi-side machining of a workpiece without the need to change in the way of holding the workpiece in appropriate position, whereby working accuracy and efficiency are improved.
Such vertical-horizontal spindle is commonly mounted on a rotating shaft, which forms a 45.degree. angle with respect to the horizontal and vertical datum lines of machine tools, whereby the rotating shaft can be adapted for leading the spindle to change into a vertical or horizontal manner.
Notwithstanding, such vertical-horizontal double-action spindle still has several shortcomings in operation. Referring to FIG. 1, the U.S. Pat. No. 4,841,795, entitled "Double-Rotatable Universal Head for Machine Tools", which relates to an application of motor mounted on machine tool through a gearing system in such a manner: gear 1.fwdarw.gear 2.fwdarw.bevel gear 3.fwdarw.bevel gear 4.fwdarw.bevel gear 5.fwdarw.bevel gear 6, for driving the mandrel 7 in rotation. More specifically, the spindle is driven by the gearing system to change into vertical or horizontal manner.
The vertical-horizontal double-action spindle of such type still needs a complicated gearing system and a long drive shaft for gearing the spindle in operation; therefore, the final structure becomes very complicated. In addition, the spindle also results in an increase in the amount of vibration, thus causing severe power loss, as a consequence the speed of the spindle is hence limited.
Referring to FIG. 2, the structure of another conventional vertical-horizontal double-action spindle, which comprises a built-in motor 8 directly driving the mandrel, and another motor 9 mounted on the distal end of the rotating shaft of said spindle for leading the spindle to change into a vertical or horizontal manner hereof. Although the spindle of this type may not require the drive shaft and gearing system, and therefore may simplify the structure and increase the speed of the spindle, the spindle has to be externally connected to a certain amount of power cable, pipelines of cooling water, lubrication oil and compressed air. Because all these pipelines are completely exposed, once the spindle is led to change into a vertical or horizontal manner, the pipelines would get swinging accordingly. Furthermore, they could get tangled to affect the operation of the spindle, as a consequence, the pipelines might easily to get polluted and damaged.
In view of this, the invention has devoted himself to the development of an improvement of spindle head for vertical-horizontal machine tools based on his experience in the research and development of related products and through continuous testing and improvement over many years.